JP4851852B2 - Master for lithographic printing plate - Google Patents

Description

  The present invention relates to a lithographic printing plate precursor, and in particular, a positive lithographic printing plate precursor for so-called direct plate making which can be directly made from a digital signal of a computer or the like, or a conventional positive lithographic printing plate compatible with UV exposure. This is related to the original version.

  Conventionally, as a positive photosensitive lithographic printing plate, an o (ortho) -quinonediazide compound and a binder resin such as a novolak resin are used as main photosensitive layer components, and after exposure to ultraviolet rays, the exposed portion is photolyzed and developed. A method for forming an image by increasing the solubility in a liquid is known. Such a positive photosensitive lithographic printing plate is usually also referred to as a conventional PS plate.

  Recently, a photothermal conversion material that absorbs infrared light, such as an infrared absorbing dye, and converts it into heat, and a binder resin such as a novolac resin are the main photosensitive layer components, and by the heat generated by infrared laser exposure, A direct plate-making method (thermal positive) and the like for changing the resin structure and increasing the solubility in a developer to form an image have been developed.

  However, the novolak resin used here has poor adhesion to the substrate due to its properties, the film is brittle, the wear resistance is inferior, and is one of the disadvantages of the conventional PS plate. In the thermal positive plate, this point is particularly emphasized, and the part that is lightly touched or lightly rubbed becomes thin during development (fingerprint missing phenomenon) or peels off (scratch phenomenon), and generally has scratches. It is said that it is easy to attach. In addition, both have poor chemical resistance, especially when UV ink is used, the printing durability is extremely inadequate, and the solvent resistance is poor with respect to UV ink roller cleaning liquid, plate surface cleaning liquid or plate cleaner, etc. There are many points that need to be improved, such as being easily missing.

  In contrast, for example, Patent Document 1 uses an acrylamide copolymer having a phenolic hydroxyl group, and Patent Document 2 and Patent Document 3 have N- (4-hydroxyphenyl) maleimide as a structural unit. Although the use of a copolymer is disclosed, none of them sufficiently satisfies the chemical resistance (solvent resistance) and the anti-fingerprint phenomenon.

Regarding the chemical resistance (solvent resistance) improvement of the thermal positive photosensitive layer, for example, Patent Document 4 discloses a lithographic printing plate precursor comprising a thermal positive photosensitive layer provided on a lower layer containing a maleimide copolymer. Although the upper layer contains a novolac resin, sufficient chemical resistance (solvent resistance) and development tolerance (development latitude) cannot be expected, and inconvenience in work such as providing two layers Have.
JP-A-62-279327 JP-A-5-88369 JP-A-2-052349 JP 2003-021902 A

  Therefore, the object of the present invention is to prevent the occurrence of the fingerprint loss phenomenon and the scratch phenomenon as described above, has excellent scratch resistance and chemical resistance (solvent resistance), and is resistant to printing even when printing using UV ink. It is intended to provide a conventional PS plate provided with a photosensitive layer excellent in printing force and a lithographic printing plate precursor for a thermal positive plate.

  As a result of intensive studies, the present inventor has found that the above object can be achieved only by one-layer coating by incorporating a specific copolymer and a specific infrared absorber in the photosensitive layer, thereby completing the present invention. It reached.

を含有する画像形成組成物
（２）前記画像形成組成物が、光を吸収して熱に変換する光熱変換物質およびアルカリ可溶性樹脂をさらに含有する前記（１）の画像形成組成物
（３）前記光熱変換物質が下記式（ＩＩＩ）で表される赤外線吸収剤である前記（２）の画像形成組成物

（式中、Ｒ₂は、各々独立して、水素原子または置換基を有してもよいアルキル基、アルコキシ基を示し、Ｒ₃は、各々独立して、置換基を有してもよいアルキル基またはアルコキシ基を示し、Ｘは電荷中和イオンを示し、ｎは５〜７を表す。）
（４）前記画像形成組成物が、キノンジアジド化合物およびアルカリ可溶性樹脂をさらに含有する前記（１）の画像形成組成物
（５）支持体上に、前記（１）〜（４）の画像形成組成物からなる感光層を有する平版印刷版用原版
That is, the present invention is as follows.
(1) Copolymer having monomer units represented by the following formulas (I) and (II)

Containing an image-forming composition
(2) The image forming composition according to (1) , wherein the image forming composition further contains a photothermal conversion substance that absorbs light and converts it into heat, and an alkali-soluble resin.
(3) The image forming composition according to (2) , wherein the photothermal conversion substance is an infrared absorber represented by the following formula (III):

(In the formula, each R ₂ independently represents a hydrogen atom or an alkyl group or an alkoxy group which may have a substituent, and R ₃ each independently represents an alkyl which may have a substituent. A group or an alkoxy group, X represents a charge neutralizing ion, and n represents 5 to 7.)
(4) The image forming composition according to (1) , wherein the image forming composition further contains a quinonediazide compound and an alkali-soluble resin.
(5) A lithographic printing plate precursor having a photosensitive layer comprising the image-forming composition described in (1) to (4) above on a support.

  As will be described in detail below, according to an original plate for a lithographic printing plate such as a direct printing plate by laser exposure and a conventional printing plate by UV exposure provided with a photosensitive layer containing a copolymer according to the present invention, both fingerprints It is possible to obtain a printing plate that is excellent in removal phenomenon and scratch resistance, has a wide development allowable width (development latitude), and is excellent in solvent resistance and printing durability even when UV ink is used.

Embodiments of the present invention will be described below. However, the embodiments described below do not limit the present invention. As described in detail below, the copolymer according to the present invention is a hydroxybenzotriazole-based compound represented by the following formula (I ′) (3- (1,2,3-benzotriazol-2-yl)- 4-hydroxyphenethyl methacrylate) and a copolymer obtained by copolymerizing N- (4-hydroxyphenyl) maleimide represented by the following formula (II ′). These components can be polymerized as necessary. It can be obtained by adding another monomer having a saturated bonding group and polymerizing in a suitable solvent using a known polymerization initiator.

  In the present invention, by containing a copolymer having a structural unit represented by formulas (I) and (II) and a specific infrared absorber, it is possible to prevent the occurrence of fingerprints and scratches, and scratch resistance. In addition, a thermal positive lithographic printing plate precursor having a photosensitive layer excellent in chemical resistance (solvent resistance) and provided with a photosensitive layer excellent in printing durability even when printing using UV ink is provided. This is because the monomers represented by the formulas (I ′) and (II ′) are difficult to dissolve in a solvent, and a copolymer containing them is a copolymer excellent in solvent resistance, As a result, the photosensitive layer containing this copolymer becomes a photosensitive layer excellent in solvent resistance. In addition, the infrared absorber represented by the formula (III) makes a high-sensitivity photosensitive layer, exhibits an effect as a dissolution inhibitor for a developer, widens a development allowable width (development latitude), and develops. It is considered to provide a photosensitive layer having excellent scratch resistance and prevention of scratch-like image loss.

  The hydroxybenzotriazole compound (3- (1,2,3-benzotriazol-2-yl) -4-hydroxyphenethyl methacrylate) represented by the formula (I ′) is, for example, methyl methacrylate and 4-ethylhydroxybenzoate. It is easily obtained by ester reaction of triazole. The compound is commercially available from Otsuka Chemical Co., Ltd. under the name RUVA-93.

  The blending ratio of the hydroxybenzotriazole compound represented by the formula (I ′) in the copolymer according to the present invention is preferably 0.5 to 50% by mass, more preferably 1 to 45% by mass of the copolymer. is there. If it is 0.5% by mass or more, particularly 1% by mass or more, chemical resistance (solvent resistance) is improved. On the other hand, when it is 50% by mass or less and 45% by mass or less, it is not excessively dissolved in the alkaline aqueous solution, and the development stability is particularly good.

  The blending ratio of N- (4-hydroxyphenyl) maleimide represented by the formula (II ′) in the copolymer is preferably 5 to 60% by mass, more preferably 10 to 55% by mass of the copolymer. It is. If it is 5% by mass or more, particularly 10% by mass or more, it is easily dissolved in an alkaline aqueous solution used as a developer, and sensitivity and chemical resistance (solvent resistance) are also improved. On the other hand, when it is 60% by mass or less, particularly 55% by mass or less, it is not excessively dissolved in the alkaline aqueous solution, and the development stability is improved.

  The total amount of the structural units represented by the formulas (I) and (II) in the copolymer is 10 to 70% by mass, more preferably 10 to 65% by mass. If it is 10% by mass or more, it is easily dissolved in an alkaline aqueous solution used as a developer, and sensitivity and chemical resistance (solvent resistance) are also improved. When it is 70% by mass or less, particularly 65% by mass or less is preferable because it does not dissolve excessively in the aqueous alkali solution.

In the above copolymer, in addition to the hydroxybenzotriazole compound represented by the formula (I ′) and the N- (4-hydroxyphenyl) maleimide represented by the formula (II ′), polymerization can be added as necessary. Examples of such other monomers include monomers exemplified in the following (1) to (10).
(1) A monomer having a phenolic hydroxyl group. For example, p-isopropenylphenol, o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, o-hydroxyphenyl acrylate, m-hydroxyphenyl acrylate, p-hydroxyphenyl acrylate, o-hydroxyphenyl methacrylate, m-hydroxy Phenyl methacrylate and p-hydroxyphenyl methacrylate.
(2) A monomer having a sulfonamide group. For example, m-aminosulfonylphenyl methacrylate, N- (p-aminosulfonylphenyl) methacrylamide, N- (p-aminosulfonylphenyl) acrylamide.
(3) A monomer having an active imide group. For example, N- (p-toluenesulfonyl) methacrylamide and N- (p-toluenesulfonyl) acrylamide.
(4) A monomer having an aliphatic hydroxyl group. For example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxy-3-phenoxypropyl methacrylate.
(5) α, β-unsaturated carboxylic acid. For example, acrylic acid, methacrylic acid, and maleic anhydride.
(6) A monomer having an allyl group. For example, allyl methacrylate and N-allyl methacrylamide.
(7) Alkyl acrylates or alkyl methacrylates. For example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, They are butyl methacrylate, amyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, and glycidyl methacrylate.
(8) Acrylamides or methacrylamides. For example, acrylamide, N-methylol acrylamide, N-ethyl acrylamide, N-hexyl acrylamide, N-cyclohexyl acrylamide, N-hydroxyethyl acrylamide, N-phenyl acrylamide, methacrylamide, N-methylol methacrylamide, N-ethyl Methacrylamide, N-hexylmethacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethylmethacrylamide, N-phenylmethacrylamide.
(9) Styrenes. For example, styrene, α-methylstyrene, chloromethylstyrene and the like.
(10) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile, methacrylonitrile and the like.
The blending ratio of the other polymerizable monomer added as necessary is preferably 30 to 90% by mass, more preferably 35 to 90% by mass of the copolymer.

  Furthermore, the copolymer is a monomer other than those which can be copolymerized with the above monomers (monomers represented by the formulas (I ′) and (II ′) and monomers exemplified in the above (1) to (10)). And a copolymer thereof. Further, a copolymer obtained by copolymerization of the above monomers may be modified with, for example, glycidyl methacrylate.

  There is no restriction | limiting in particular about the manufacturing method of the said copolymer, It can manufacture similarly to the manufacturing method of a normal acrylic copolymer. For example, a desired copolymer can be obtained by dissolving each monomer component in a suitable solvent, adding a conventionally used radical polymerization initiator, and performing polymerization by heating as necessary. The copolymer thus obtained has a polystyrene calculated weight average molecular weight of 1000 to 200,000, preferably 2000 to 100,000,000, as measured by gel permeation chromatography (GPC). It is done. When the average molecular weight is 1000 or more, particularly 2000 or more, the copolymer has a particularly excellent solvent resistance, and when the average molecular weight is 200,000 or less, particularly 100,000 or less, a photosensitive solution is applied. This is because it dissolves particularly well in the solvent.

  Although not particularly limited, the solvent used for the polymerization of the copolymer includes methyl cellosolve, propylene glycol monomethyl ether, dioxane, methyl ethyl ketone, cyclohexanone, N, N-dimethylformamide, N, N -Dimethylacetamide etc. are mentioned. Examples of the radical polymerization initiator used for the polymerization of the copolymer include 2,2'-azobis (2-methylbutyronitrile), benzoyl peroxide, and the like. As addition amount, it is 0.1-1.0 mass% with respect to the whole quantity of a monomer. When heating at the time of superposition | polymerization, about 40-130 degreeC is generally preferable for heating temperature.

  In the present invention, the content of the copolymer is preferably 3 to 90% by mass, more preferably 5 to 85% by mass of the photosensitive layer. When the addition amount is 3% by mass or more, particularly 5% by mass or more, chemical resistance (solvent resistance) is particularly good. When the addition amount is 90% by mass or less, particularly 85% by mass or less, poor development or stability over time is deteriorated. Disappears.

The photothermal conversion substance used in the present invention is not particularly limited as long as it is a compound that can absorb light from an image exposure light source and convert the energy into heat, but has an absorption maximum in a wavelength range of 650 to 1300 nm. An infrared absorbing dye having an absorption maximum and a molar extinction coefficient ε of 10 ⁵ or more is particularly effective. The photothermal conversion substance is used for causing a physical change such as a structural change of a resin by heat generated from the photothermal conversion substance by light irradiation and increasing the solubility in a developer. For this reason, the photosensitive layer of the present invention becomes a positive photosensitive layer that further contains a photothermal conversion substance, so that the solubility in an alkaline aqueous solution is increased by laser exposure.

  Examples of the infrared absorbing dye include a cyanine dye, a squalium dye, a croconium dye, an azurenium dye, a phthalocyanine dye, a naphthalocyanine dye, a polymethine dye, a naphthoquinone dye, a thiopyrylium dye, a dithiol metal complex dye, Anthraquinone dyes, indoaniline metal complex dyes, intermolecular CT dyes and the like are preferable.

Although these pigment | dyes can be synthesize | combined by a well-known method, the following commercial items can also be used.
Nippon Kayaku Co., Ltd .: IR750 (anthraquinone), IR002, IR003 (aluminum), IR820 (polymethine), IRG022, IRG033 (diimmonium), CY-2, CY-4, CY-9, CY-10, CY-20
Dai Nippon Ink Chemical Co., Ltd .: Fastogen blue 8120
Midori Chemical Co., Ltd .: MIR-101, 1011 and 1021
In addition, the above dyes are also commercially available from various companies such as Nippon Photosensitive Co., Ltd., Sumitomo Chemical Co., Ltd., and Fuji Photo Film Co., Ltd.

（式中、Ｒ₂は水素原子または置換基を有してもよいアルキル基、アルコキシ基を示し、Ｒ₃は置換基を有してもよいアルキル基またはアルコキシ基を示し、Ｘは電荷中和イオンを示し、ｎは５〜７を表す。） Among the infrared absorbing dyes, an infrared absorber represented by the following general formula (III) is particularly preferable.

(In the formula, R ₂ represents a hydrogen atom or an optionally substituted alkyl group or alkoxy group, R ₃ represents an optionally substituted alkyl group or alkoxy group, and X represents charge neutralization. Represents an ion, and n represents 5 to 7.)

  Although the preferable specific example of the infrared absorber represented by the said general formula (III) is shown below, the range of the compound is not limited to these.

  In the present invention, the amount of the photothermal conversion substance added is 0.5 to 10% by mass, preferably 0.6 to 8.0% by mass of the photosensitive layer. When the addition amount is 0.5% by mass or more, particularly 0.6% by mass or more, the sensitivity is particularly high. Since it improves especially, it is preferable.

  In the present invention, the alkali-soluble resin is used in the thermal positive plate to improve the printing durability and the ink landing property in an unexposed portion (image portion). The alkali-soluble resin used in the present invention is desirably soluble or swellable with respect to an alkali agent. Examples of such a polymer compound include novolac resins, resole resins, polyvinylphenol resins, and copolymers of acrylic acid derivatives. Note that the alkali-soluble resin is well dissolved in an alkaline developer after exposure. Further, the alkali-soluble resin is partially dissolved in an alkaline developer before exposure, depending on conditions such as the alkali concentration of the developer, the temperature of the developer, and the development time.

  As the novolak resin, phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, resorcin, pyrogallol, bisphenol, bisphenol A, trisphenol, o-ethylphenol, m- At least one of aromatic hydrocarbons such as ethylphenol, p-ethylphenol, propylphenol, n-butylphenol, t-butylphenol, 1-naphthol, 2-naphthol and the like in the form of an acidic catalyst, formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde , Aldehydes such as furfural, and those obtained by polycondensation with ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone can be used.

  Paraformaldehyde and paraaldehyde may be used in place of formaldehyde and acetaldehyde, respectively. The polystyrene calculated weight average molecular weight (hereinafter abbreviated as Mw) by gel permeation chromatography (GPC) measurement of novolak resin is preferably 1,000 to 20,000, particularly preferably 1,500 to 15,000. It is done.

  Examples of commercially available novolak resins include PSF-2803, PSF-2807 (manufactured by Gunei Chemical Industry Co., Ltd.), EP4020GS, EP5020G, EP6020G (manufactured by Asahi Organic Materials Co., Ltd.), Hitanol 1501 (manufactured by Hitachi Chemical Co., Ltd.), BRM- 565 (manufactured by Showa Polymer Co., Ltd.), RV-95, RT-95 (manufactured by Gifu Shellac Co., Ltd.) and the like can be used.

Polyvinylphenol resins include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, 2- (o-hydroxyphenyl) propylene, 2- (m-hydroxyphenyl) propylene, 2- (p-hydroxyphenyl) propylene. Examples thereof include hydroxystyrenes alone or two or more polymers. Hydroxystyrenes may have a substituent such as a halogen such as chlorine, bromine, iodine, fluorine or a C ₁ -C ₄ alkyl substituent in the aromatic ring. or include good polyvinyl phenols have an alkyl substituent of C ₁ -C _4.

  The polyvinylphenol resin is usually obtained by polymerizing hydroxystyrenes which may have a substituent, alone or in the presence of a radical polymerization initiator or a cationic polymerization initiator. Such polyvinyl phenol resin may be partially hydrogenated. Further, a resin in which a part of OH groups of polyvinylphenols are protected from a t-butoxycarbonyl group, a pyranyl group, a furanyl group, or the like may be used. The Mw of the polyvinylphenol resin is preferably 1,000 to 80,000, particularly preferably 1,500 to 50,000.

  When the Mw of the above novolak resin or polyvinylphenol resin is larger than the lower limit of the above range, a particularly sufficient coating film can be obtained, and the printing durability is improved. Especially the solubility with respect to becomes good, and it becomes difficult to cause soiling.

As a copolymer of acrylic acid derivatives, a monomer selected from the following (m1) to (m10) is copolymerized using a conventionally known graft copolymerization method, block copolymerization method, random copolymerization method, or the like. Can be obtained.
(M1) A monomer having a phenolic hydroxyl group. For example, N- (4-hydroxyphenyl) acrylamide, N- (4-hydroxyphenyl) methacrylamide, p-isopropenylphenol, o-hydroxyphenyl acrylate, m-hydroxyphenyl acrylate, p-hydroxyphenyl acrylate, o-hydroxy Phenyl methacrylate, m-hydroxyphenyl methacrylate, and p-hydroxyphenyl methacrylate.
(M2) A monomer having a sulfonamide group. For example, m-aminosulfonylphenyl methacrylate, N- (p-aminosulfonylphenyl) methacrylamide, N- (p-aminosulfonylphenyl) acrylamide.
(M3) A monomer having an active imide group. For example, N- (p-toluenesulfonyl) methacrylamide and N- (p-toluenesulfonyl) acrylamide.
(M4) A monomer having an aliphatic hydroxyl group. For example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxy-3-phenoxypropyl methacrylate.
(M5) α, β-unsaturated carboxylic acid. For example, acrylic acid, methacrylic acid, and maleic anhydride.
(M6) A monomer having an allyl group. For example, allyl methacrylate and N-allyl methacrylamide.
(M7) Alkyl acrylates or alkyl methacrylates. For example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, They are butyl methacrylate, amyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, and glycidyl methacrylate.
(M8) Acrylamides or methacrylamides. For example, acrylamide, N-methylol acrylamide, N-ethyl acrylamide, N-hexyl acrylamide, N-cyclohexyl acrylamide, N-hydroxyethyl acrylamide, N-phenyl acrylamide, methacrylamide, N-methylol methacrylamide, N-ethyl Methacrylamide, N-hexylmethacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethylmethacrylamide, N-phenylmethacrylamide.
(M9) Styrenes. For example, styrene, α-methylstyrene, chloromethylstyrene and the like.
(M10) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile, methacrylonitrile and the like.

  The Mw of the acrylic acid derivative copolymer is preferably 1,000 to 500,000, particularly preferably 1,500 to 300,000. When the Mw is 1,000 or more, particularly 1,500 or more, a particularly sufficient coating film can be obtained. When the Mw is 500,000 or less, particularly 300,000 or less, the solubility of the exposed portion in the alkaline developer is improved and particularly good. Can be developed.

  The alkali-soluble resins used in the present invention may be used alone or in combination of two or more. The addition amount is 1 to 80% by mass, preferably 5 to 70% by mass, based on the photosensitive layer. When the addition amount is less than 1% by mass, the printing durability may be deteriorated, and when it is 80% by mass or more, the solvent resistance may be deteriorated.

  In the present invention, the quinonediazide compound is used for photolysis by ultraviolet rays or the like, chemically changing to indenecarboxylic acid, and increasing the solubility in an alkaline aqueous solution as a developer. For this reason, the photosensitive layer of this invention becomes a positive type photosensitive layer by which the solubility with respect to alkaline aqueous solution increases by UV exposure by containing a quinonediazide compound further. Examples of the quinonediazide compound include ester compounds of naphthoquinone-1,2-diazide-5-sulfonyl chloride or naphthoquinone-1,2-diazide-4-sulfonyl chloride and a compound having a phenolic hydroxyl group.

  Examples of the compound having a phenolic hydroxyl group include phenol, o-cresol, m-cresol, p-cresol, pt-butylphenol, catechol, resorcinol, hydroquinone, pyrogallol, bisphenol A, bisphenol S, hydroxybenzophenone, and polyvalent hydroxy. Benzophenone or a polycondensation resin of these phenols with an aldehyde or a ketone can be used.

  Preferred examples of the polycondensation resin include phenol / formaldehyde resin, o-cresol / formaldehyde resin, m-cresol / formaldehyde resin, p-cresol / formaldehyde resin, m / p-mixed cresol / formaldehyde resin, t-butylphenol / formaldehyde. Resin, bisphenol A / formaldehyde resin, bisphenol S / formaldehyde resin, pyrogallol / formaldehyde resin, pyrogallol / acetone resin, hydroxybenzophenone / formaldehyde resin, polyvalent hydroxybenzophenone / formaldehyde resin, and the like.

  The ester compound of the naphthoquinonediazide compound and the compound having a phenolic hydroxyl group, that is, the quinonediazide compound used in the present invention can be synthesized by a conventionally known synthesis method. For example, dioxane, acetone or the like is used as a solvent, and naphthoquinone diazide sulfonyl chloride and a compound having a phenolic hydroxyl group are added thereto, and an ester such as sodium carbonate, sodium hydrogen carbonate, triethylamine is added dropwise to the equivalent point for esterification. .

  The content of the quinonediazide compound in the photosensitive layer of the present invention is preferably 5 to 60% by mass, more preferably 10 to 50% by mass. When the content is 5% by mass or more, particularly 10% by mass or more, the development latitude (development width) such as the disappearance of the image portion during development is eliminated. Therefore, it is preferable.

  In addition to the components described above, the photosensitive layer of the present invention may further include an acid generator, a colorant, a grease-sensitive resin, a sensitivity improver, a development dissolution inhibitor, a plasticizer, as long as the effects of the present invention are not impaired. An agent or the like can be added.

The acid generator is a compound capable of generating an acid when the lithographic printing original plate of the present invention is irradiated with light. That is, as described above, when light is irradiated on the lithographic printing original plate, the photothermal conversion substance can instantaneously generate heat of, for example, several hundred degrees by absorbing this light. An acid generator is a compound that can be decomposed by the heat generated to generate an acid. As such an acid generator, for example, BF ₄ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , SiF ₆ ²⁻ , ClO ₄ ^{− and the} like of diazonium, phosphonium, sulfonium, and iodonium are preferable.

  Moreover, an organic halogen compound can be used as another photoacid generator. As the organic halogen compound, triazines having a halogen-substituted alkyl group and oxadiazoles having a halogen-substituted alkyl group are preferable, and s-triazines having a halogen-substituted alkyl group are particularly preferable. Although not particularly limited, specifically, 2- (p-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (p-methoxynaphthyl) -4,6- And bis (trichloromethyl) -s-triazine, 2- (p-methoxystyryl) -4,6-bis (trichloromethyl) -s-triazine, and the like.

  In the present invention, the addition amount of the acid generator is preferably 0.1 to 20% by mass, more preferably 0.2 to 15% by mass of the photosensitive layer. When the addition amount is 0.1% by mass or more, particularly 0.2% by mass or more, the sensitivity does not particularly deteriorate the sensitivity. It becomes easy.

  In the photosensitive layer according to the present invention, a colorant can be used to make the image easy to see. As the colorant, oil-soluble dyes and basic dyes are preferable. Specifically, Crystal Violet, Malachite Green, Victoria Blue, Methylene Blue, Ethyl Violet, Rhodamine B, Victoria Pure Blue BOH (Hodogaya Chemical Industries), Oil Blue 613 (Orient Chemical Industries), Oil Green, etc. Can be mentioned. The addition amount of these dyes is preferably 0.05 to 5.0% by mass of the photosensitive layer, and more preferably 0.1 to 4.0% by mass. If it is 0.05% by mass or more, particularly 0.1% by mass or more, the photosensitive layer is sufficiently colored and the image is particularly easy to see. If it is 5.0% by mass or less, particularly 4.0% by mass or less, a non-image after development. The remainder of the dye is difficult to remain in the part, which is preferable.

  Furthermore, a fat-sensitive resin can be added to the photosensitive layer of the present invention in order to improve the grease sensitivity (lipophilicity) of the photosensitive layer. Examples of the fat-sensitive resin include condensates of phenols and aldehydes substituted with an alkyl group having 3 to 15 carbon atoms, or t-butylphenol formaldehyde resin as described in JP-A No. 50-125806. Etc. can be used.

  Examples of sensitivity improvers that can be used in the present invention include cyclic acid anhydrides, phenols, and organic acids. Examples of the cyclic acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, succinic anhydride, pyromellitic anhydride, and the like.

  Examples of phenols include bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 4-hydroxybenzophenone, 4,4 ′, 4. '' -Trihydroxytriphenylmethane, 4,4 ′, 3 ″, 4 ″ -tetrahydroxy-3,5,3 ′, 5′-tetramethyltriphenylmethane and the like are preferable.

  Examples of organic acids include sulfonic acids, sulfinic acids, alkyl sulfates, phosphonic acids, phosphate esters, and carboxylic acids described in JP-A-60-88942 and JP-A-2-96755. Specifically, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethyl sulfate, phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipine Acid, p-toluic acid, 3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid, ascorbic acid, etc. It is done.

  The proportion of the sensitivity improver such as cyclic acid anhydrides, phenols, and organic acids in the photosensitive layer is preferably 0.05 to 20% by mass, more preferably 0.1 to 15% by mass, and particularly preferably. Is 0.1 to 10% by mass.

  The development dissolution inhibitor that can be used in the present invention is preferably an alkylphenol resin, polyethylene glycol, leuco dye, or surfactant.

  As specific examples of the alkylphenol resin, PS-2821, PS-4609, PS-2820, PS-4900 manufactured by Gunei Chemical Industry Co., Ltd., CKM-908, CKM-2400 manufactured by Showa Polymer Co., Ltd., and the like are preferable.

  As the leuco dye, a dye containing a lactone ring used in conventional heat-sensitive recording materials is preferable. Preferred examples include 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3- Bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3,3- Bis (p-diethylamino-2-ethoxyphenyl) -4-azaphthalide, 3,6-dimethoxyfluorane, 3-cyclohexylamino-6-chlorofluorane, 3- (N, N-diethylamino) -5-methyl-7 -(N, N-dibenzylamino) fluorane, 3-dimethylamino-5, 7-dimethylfluorane, 3 Dimethylamino-7-methylfluorane, 3-diethylamino-7, 8-benzfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chloroaminofluorane, 3-pyrrolidino- 6-methyl-7-anilinofluorane, 3-dimethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 2- (N- (3 And '-trifluoromethylphenyl) amino) -6-diethylaminofluorane, 2- (3,6-bis (diethylamino) -9- (o-chloroanilino) xanthyl benzoate lactam, and the like.

  Surfactants as development inhibitors include nonionic surfactants such as those described in JP-A-62-251740 and JP-A-3-208514, JP-A-59-121044, Amphoteric surfactants as described in JP-A-4-13149 are preferred. Preferable examples of the nonionic surfactant include sorbitan tristearate, sorbitan monopalmitate, sorbitan trioleate, stearic acid monoglyceride, polyoxyethylene nonylphenyl ether and the like. Preferred examples of the amphoteric surfactant include alkyldi (aminoethyl) glycine, alkylpolyaminoethylglycine hydrochloride, 2-alkyl-N-carboxyethyl-N-hydroxyethylimidazolinium betaine, and N-tetradecyl-N, N- Examples include betaine type (for example, trade name “Amorgen K” manufactured by Daiichi Kogyo Co., Ltd.).

  The proportion of the development inhibitor in the photosensitive layer is preferably 0.05 to 15% by mass, and more preferably 0.1 to 15% by mass. When it is 0.05% by mass or more, particularly 0.1% by mass or more, the developability is particularly good, and when it is 15% by mass or less, the developability is not slowed.

  A plasticizer can be added to the photosensitive layer of the present invention in order to impart flexibility and the like of the coating film. For example, butylphthalyl, tributyl citrate, diethyl phthalate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, tricresyl phosphate, trioctyl phosphate, tributyl phosphate and the like are used.

  Improves detachability between plates when a large number of lithographic printing original plates of the present invention are stacked without interleaving paper, and also improves detachability between interleaving paper and plate even when interleaving interleaving paper Therefore, the surface of the photosensitive layer of the lithographic printing original plate may be matted in order to prevent vacuum blurring at the time of close exposure with the original image film. As a method for matting the surface of the photosensitive layer, a method of adding a matting agent or the like to the image forming composition of the present invention, a solution in which a water-soluble resin or a water-soluble resin and a matting agent are dissolved and dispersed on the surface of the photosensitive layer. There are methods such as spray coating. Examples of the matting agent include silicon dioxide, zinc oxide, titanium oxide, alumina powder, starch, starch, polymer particles (for example, particles such as polyacrylic acid and polystyrene), and the like.

  In the photosensitive layer of the present invention, a photosensitive lithographic printing plate precursor can be produced by dissolving the above components in a solvent and coating a photosensitive layer coating solution (photosensitive solution) on a suitable support. Solvents used here include methanol, ethanol, propanol, methylene chloride, ethyl acetate, tetrahydrofuran, propylene glycol monomethyl ether, propylene glycol monoethyl ether, methyl cellosolve, ethyl cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, N, N Examples include, but are not limited to, -dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, dioxane, dioxolane, acetone, cyclohexanone, trichloroethylene, methyl ethyl ketone, and γ-butyllactone. These solvents are used alone or in combination of two or more. The concentration of the above components (total solid content including additives) in the solvent is preferably 1 to 50% by mass.

Various methods can be used as the coating method, and examples thereof include spin coating, extrusion coating, bar coater coating, roll coating, air knife coating, dip coating, and curtain coating. The coating amount of the photosensitive layer varies depending on the use, but is preferably 0.5 to 5.0 g / m ² at the time of drying.

  Examples of the support include a metal plate such as aluminum, zinc, copper, or steel, a metal plate plated or vapor-deposited with chromium, zinc, copper, nickel, aluminum, iron, or the like, paper, plastic film, or glass. Examples thereof include a plate, paper coated with a resin, and a plastic film subjected to a hydrophilic treatment.

  As the support of the present invention, a polyester film or an aluminum plate is preferable, and among them, an aluminum plate that has good dimensional stability and is relatively inexpensive is particularly preferable. A suitable aluminum plate is a pure aluminum plate or an alloy plate containing aluminum as a main component and containing a trace amount of foreign elements, and may be a plastic film on which aluminum is laminated or vapor-deposited. Thus, the composition of the aluminum plate applied to the present invention is not specified, and a conventionally known and publicly available aluminum plate can be appropriately used. The thickness of the aluminum plate used in the present invention is approximately 0.1 to 0.5 mm, preferably 0.12 to 0.4 mm.

  Prior to roughening the aluminum plate, a degreasing treatment with, for example, a surfactant or an alkaline aqueous solution for removing rolling oil on the surface is performed. The surface roughening treatment of the surface of the aluminum plate is performed by various methods. For example, a method of mechanically roughening, a method of electrochemically roughening the surface, and a method of selectively dissolving the surface chemically. By the method. As the mechanical method, known methods such as brush polishing, ball polishing, blast polishing, and buff polishing can be used. Further, as an electrochemical surface roughening method, there is a method of performing alternating current or direct current in hydrochloric acid or nitric acid electrolyte. Further, a method combining a mechanical method and an electrochemical method disclosed in JP-A-53-123204 can also be used. The roughened aluminum plate is subjected to alkali etching treatment and neutralization treatment as necessary, and then subjected to anodization treatment to enhance the surface water retention and wear resistance as desired. In general, sulfuric acid, phosphoric acid, oxalic acid, chromic acid or a mixed acid thereof is used as an electrolyte used for anodizing the aluminum plate.

The treatment conditions for anodization vary depending on the electrolyte used and thus cannot be specified in general. In general, however, the electrolyte concentration is 1 to 60% by mass solution, the liquid temperature is 5 to 60 ° C., and the current density is 2 to 50 A / dm ² , voltage 1 to 100 V, and electrolysis time 5 seconds to 3 minutes are suitable. If the amount of anodic oxide film is 0.5 to 5.0 g / ^{m 2} is suitable, wear resistance is especially good at 0.5 g / ^{m 2} or more, the 5.0 g / ^{m 2} or less, the pores of the anodic oxidation Dyes and the like are particularly preferred because they are difficult to penetrate.

  After the anodization, the aluminum plate is further subjected to a chemical conversion treatment with, for example, an alkali silicate, sodium phosphate, sodium fluoride, zirconium fluoride, alkyl titanate, trihydroxybenzoic acid alone or in a mixed solution, Sealing treatment by immersion in an aqueous solution or steam bath, coating treatment with an aqueous solution such as strontium acetate, zinc acetate, magnesium acetate, or calcium benzoate, polyvinylpyrrolidone, polyaminesulfonic acid, polyvinylphosphonic acid, polyacrylic acid, Alternatively, chemical conversion or coating treatment of the front or back surface with polymethacrylic acid or the like can be performed as a post-treatment.

  Furthermore, as the above-mentioned support, an aluminum support subjected to the surface treatment described in JP-A-10-297130 can be used.

  As a laser light source for irradiating the lithographic printing plate precursor according to the present invention, a light source having an emission wavelength in the near infrared to infrared region is preferable, and a solid laser or a semiconductor laser is preferable. The emission wavelength is preferably 760 to 1300 nm. Examples of the light source for UV exposure include a carbon arc lamp, a mercury lamp, a metal halide lamp, a xenon lamp, and a chemical lamp. The emission wavelength is preferably 300 to 500 nm.

  As the developer and developer replenisher used for the development of the lithographic printing original plate of the present invention, an aqueous alkaline developer is suitable. Alkaline agents include sodium hydroxide, potassium, ammonium, lithium, sodium silicate, potassium, ammonium, lithium, tribasic sodium phosphate, potassium, ammonium, sodium borate, potassium, Inorganic alkali agents such as ammonium and sodium carbonate, and organic alkalis such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, sodium octoate, and tetramethylammonium hydroxide Agents and the like. These alkali agents may be used alone or in combination of two or more.

  An activator can be further added to the alkaline aqueous solution. As the activator, an anionic surfactant or an amphoteric surfactant can be used.

  Examples of the ionic surfactant include sulfates of alcohols having 8 to 22 carbon atoms (for example, polyoxyethylene alkyl sulfate soda salt), alkyl aryl sulfonates (for example, sodium dodecylbenzenesulfonate, polyoxyethylene dodecylphenyl sulfate). Soda salt, alkyl naphthalene sulfonic acid soda, naphthalene sulfone soda, formalin condensate of naphthalene sulfone soda), sodium dialkyl sulfonate, alkyl ether phosphate, alkyl phosphate, and the like can be used. In addition, as the amphoteric surfactant, for example, alkylbetaine type and alkylimidazoline type surfactants are preferable. Furthermore, for example, water-soluble sulfites such as sodium sulfite, potassium sulfite, lithium sulfite, and magnesium sulfite can be added to the alkaline aqueous solution.

  The present invention will be described more specifically with reference to the following examples. However, the present examples do not limit the present invention.

[Synthesis of Copolymer (I to III) and Comparative Copolymer I (Comparative I)]
To a 1 L four-necked flask equipped with a stirrer and a condenser, 200 g of N, N-dimethylformamide as a reaction solvent and a mixture of each structural unit shown in Table 1 below were added. After heating the inside of the flask to 90 ° C., 0.4 g of 2,2′-azobis (2-methylbutyronitrile) was added, and after replacing with nitrogen gas, the mixture was stirred at 90 ° C. for 5 hours. After completion of the reaction, the reaction mixture was poured into 10 L of water, filtered and dried.

ＲＵＶＡ−９３：（３−（１、２、３−ベンゾトリアゾール−２−イル）−４−ヒドロキシフェネチルメタクリレート）
Ｎ−ＨＰＭＩ：Ｎ−（４−ヒドロキシフェニル）マレイミド
ＡＮ：アクリロニトリル
ＭＭＡ：メチルメタクリレート

RUVA-93: (3- (1,2,3-benzotriazol-2-yl) -4-hydroxyphenethyl methacrylate)
N-HPMI: N- (4-hydroxyphenyl) maleimide AN: Acrylonitrile MMA: Methyl methacrylate

[Synthesis of Comparative Copolymer II]
Copolymer No. 1 described in Patent Document 3 (Japanese Patent Laid-Open No. 2-0534949). It was synthesized by the same method as that of the above-mentioned copolymer I using the following monomer monomers similar to 17.
Monomer No. 1 (N- (3,5-dimethyl-4-hydroxyphenyl) methylacrylamide / N- (4-hydroxyphenyl) maleimide / styrene = 15/40/45 (mol%)

[Production of support]
An aluminum plate (material 1050) having a thickness of 0.24 mm was degreased with alkali, then the surface was polished with a nylon brush while applying a water suspension of palmiston, and washed thoroughly with water. Next, 70 ° C., 15% by mass aqueous sodium hydroxide solution was applied for 5 seconds, the surface was etched at 3 g / m ² , then further washed with water, and then electrolytically roughened at 200 coulomb / dm ² in a 1N hydrochloric acid bath. Processed. Subsequently, the surface was etched again with a 15% by mass aqueous sodium hydroxide solution, washed with water, and then immersed in a 20% by mass nitric acid aqueous solution for desmutting. Next, anodization was performed in a 15% by mass sulfuric acid aqueous solution to form a 1.8 g / m ² oxide film. After washing with water, 1% by mass potassium fluoride at 50 ° C. and 10% by mass phosphoric acid. It was post-treated with a mixed solution of monosodium, washed with water and dried.

[Examples 1 to 3]
Next, three types of photosensitive solutions A to C were prepared by changing the type of the copolymer of the present invention in the following photosensitive solutions. These photosensitive solutions were applied onto the aluminum support so that the film thickness after drying was 2.0 g / m ² and dried at 100 ° C. for 10 minutes to obtain a lithographic printing plate. The copolymers of the present invention used for the photosensitive solutions a to c are shown in Table 2 below.

(Sensitive solution A to C)
Copolymer of the present invention (3.5 g)
Novolac resin (PSF-2803) (manufactured by Gunei Chemical Industry Co., Ltd.) (1.0 g)
Novolac resin (PSF-2807) (manufactured by Gunei Chemical Industry Co., Ltd.) (0.5 g)
Infrared absorber: Infrared absorber (3) (0.35 g)
Acid generator: 2- (p-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine (0.02 g)
Dissolution inhibitor: Polyethylene glycol # 4000 (0.2 g)
Dye: Oil Blue 613 (Orient Kogyo Co., Ltd.) (0.05 g)
Solvent: methyl cellosolve (20 g)
N, N-dimethylformamide (5 g)
Propylene glycol monomethyl ether (5g)

[Comparative Examples 1-2]
Next, as comparative examples, photosensitive solutions D and E were prepared in the same manner as in Examples 1 to 3, using Comparative Copolymers I and II in place of the copolymer according to the present invention. These photosensitive solutions were applied onto an aluminum plate in the same manner as in Example 1 to prepare a lithographic printing plate. The comparative copolymers used in the photosensitive solutions d and e are shown in Table 2.

[Comparative Example 3]
As a comparative example, the following photosensitive solution containing no copolymer according to the present invention was prepared, and this photosensitive solution was applied on an aluminum plate in the same manner as in Example 1 to prepare a lithographic printing plate.

(Photosensitive solution)
Novolac resin (PSF-2803) (manufactured by Gunei Chemical Industry Co., Ltd.) (4.5 g)
Novolac resin (PSF-2807) (manufactured by Gunei Chemical Industry Co., Ltd.) (0.5 g)
Infrared absorber: Infrared absorber (3) (0.35 g)
Acid generator: 2- (p-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine) (0.02 g)
Dissolution inhibitor: Polyethylene glycol # 4000 (0.2 g)
Dye: Oil Blue 613 (Orient Kogyo Co., Ltd.) (0.05 g)
Solvent: methyl cellosolve (20 g)
N, N-dimethylformamide (5 g)
Propylene glycol monomethyl ether (5g)

[Performance evaluation of planographic printing plates]
For the lithographic printing plates of Examples 1 to 3 and Comparative Examples 1 to 3 prepared as described above, performance evaluation was performed according to the following criteria.

[Evaluation of fingerprint loss and scratch resistance]
The obtained lithographic printing plate was imaged with an exposure amount of 100 mJ / cm ^{2 in} an image using a plate setter (manufactured by Creo: Trend Setter 400QTM) having a semiconductor laser with a wavelength of 830 nm. Thereafter, a portion where the unexposed portion (solid image portion) was rubbed with a finger and a portion where the surface of the image was run with a 5 μm diameter needle on which a 5 g weight was placed were made. Next, the film was developed with an automatic developing machine (PK-1310II) charged with a thermal positive developer TD-4 (dilution ratio 1: 9, liquid temperature 30 ° C.) manufactured by Okamoto Chemical Co., Ltd., with an immersion time of 12 seconds. The degree of film reduction in the solid image portion and the degree of image peeling (scratched state) are evaluated. The results are shown in Table 2 below.

[Evaluation of printing durability with UV ink]
The lithographic printing plate was printed on high-quality paper using UV ink (manufactured by Toyo Ink Co., Ltd., flash dry ink APN). At this time, an operation of rubbing the plate surface with the best cure plate cleaning solution manufactured by T & K and TOKA every 1000 parts was added. When the number of printed sheets until the solid portion was scraped was examined, it was as shown in Table 2 below.

[Solvent resistance evaluation]
The printing plate UV ink washing liquid Dicure oil washing A (Dainippon Ink & Chemicals, Inc.) stock solution is immersed, and the time until the image portion is attacked and melted is compared. The results are shown in Table 2 below.

評価基準；指紋抜け：○画像部に異常見られず。
△指で擦った部分の画像ベタ部が点々状に薄くなる。
×指で擦った部分の画像ベタ部が半分程薄くなる。
耐キズ性：○画像部に異常見られず。
△僅かに針の跡が見える。
×針で画いた直線状に画像がハガれる。

Evaluation criteria: Fingerprint missing: No abnormality is observed in the image area.
Δ The solid image portion of the portion rubbed with a finger becomes thin and dotted.
X The solid image portion of the portion rubbed with a finger becomes half thinner.
Scratch resistance: ○ No abnormality is observed in the image area.
ΔSlight traces of needles are visible.
X The image is drawn in a straight line drawn with the needle.

Evaluation of development allowable width (development latitude) Each lithographic printing plate of Examples 1 to 3 and Comparative Examples 1 to 3 is drawn in an image with an exposure amount of 100 mJ / cm ^{2 on} the plate setter, and the same as above. In a thermal positive developer TD-4 (dilution ratio 1: 9, liquid temperature 30 ° C.), a time until a halftone dot corresponding to 175 lines and 3% was reproduced and disappeared (development allowable width) was measured. The results are shown in Table 3.

[Examples 4 to 6]
Three types of photosensitive solutions were prepared by changing the type of the copolymer of the present invention in the following photosensitive solutions. These photosensitive solutions were applied onto the aluminum plate in the same manner as in Example 1 using a 0.2 mm wire diameter wire bar so that the film thickness after drying was 2.0 g / m ^2. And dried for 10 minutes to obtain planographic printing plates of Examples 4 to 6. The copolymers of the present invention used for the photosensitive solution are shown in Table 4.

(Photosensitive solution)
Copolymer of the present invention (6.0 g)
Novolac resin (PSF-2803) (manufactured by Gunei Chemical Industry Co., Ltd.) (0.5 g)
Novolac resin (PSF-2807) (manufactured by Gunei Chemical Industry Co., Ltd.) (0.5 g)
Ester compound of naphthoquinone-1,2-diazide-5-sulfonyl chloride and pyrogallol / acetone resin (2.5 g)
2- (p-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine (0.1 g)
Dye: Oil blue 613 (manufactured by Orient Kogyo) (0.2 g)
Solvent: methyl cellosolve (50 g)
N, N-dimethylformamide (25 g)
Propylene glycol monomethyl ether (25g)

[Comparative Examples 4 and 5]
Next, as a comparative example, a photosensitive solution was prepared in the same manner as in Example 4 using the comparative copolymers I and II instead of the copolymer according to the present invention in the above photosensitive solution. These sensitizing solutions were applied onto the same aluminum plate as used in Example 1 to prepare lithographic printing plates of Comparative Examples 4 and 5. The comparative copolymers used for the photosensitive solutions are shown in Table 4.

[Comparative Example 6]
As a comparative example, the following photosensitive solution was prepared, and this photosensitive solution was applied on the same aluminum plate as used in Example 1 to prepare a lithographic printing plate of Comparative Example 6.

(Photosensitive solution)
Novolac resin (PSF-2803) (manufactured by Gunei Chemical Industry Co., Ltd.) (3.5 g)
Novolac resin (PSF-2807) (manufactured by Gunei Chemical Industry Co., Ltd.) (3.5 g)
Ester compound of naphthoquinone-1,2-diazide-5-sulfonyl chloride and pyrogallol / acetone resin (2.5 g)
2- (p-methoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine (0.1 g)
Dye: Oil blue 613 (manufactured by Orient Kogyo) (0.2 g)
Solvent: methyl cellosolve (50 g)
N, N-dimethylformamide (25 g)
Propylene glycol monomethyl ether (25g)

[Performance evaluation of planographic printing plates]
For the lithographic printing plates of Examples 4 to 6 and Comparative Examples 4 to 6 prepared as described above, performance evaluation was performed according to the following criteria.

[Evaluation of fingerprint loss]
The obtained lithographic printing plate was baked with a test pattern for about 60 seconds at a distance of 1 m using a UV exposure machine (Kuranami Co., Ltd.) equipped with a 3 KW metal halide lamp. I rubbed the part with a finger or deliberately created a place where the finger was pressed. Next, a developer No. 1 for Sylvan Positive manufactured by Okamoto Chemical Co., Ltd. Developed with an automatic processor (PK-1310II) charged with a 12-fold diluted solution of 4. The degree of film reduction in the solid image portion and the flat mesh portion was evaluated. The results are shown in Table 4 below.

[Evaluation of printing durability with UV ink]
The lithographic printing plate was printed on high-quality paper using UV ink (manufactured by Toyo Ink Co., Ltd., flash dry ink APN). At this time, an operation of rubbing the plate surface with the best cure plate cleaning solution manufactured by T & K and TOKA every 1000 parts was added. When the number of printed sheets until the solid portion was scraped was examined, it was as shown in Table 4 below.

[Solvent resistance evaluation]
The printing plate was immersed in a stock solution of UV ink washing liquid Dicure washing A (manufactured by Dainippon Ink and Chemicals), and the time until the image area was attacked and dissolved was compared. The results are shown in Table 4 below.

評価基準；指紋抜け：○画像部に異常見られず。
△指で擦った部分の画像ベタ部が半分程膜減りを起こした。
×平網部分では、指紋状に膜減りした。

Evaluation criteria: Fingerprint missing: No abnormality is observed in the image area.
Δ The film was thinned by about half of the solid image portion rubbed with a finger.
× At the flat mesh portion, the film was reduced to a fingerprint.

  As is apparent from Tables 1 to 4, according to the direct printing plate by laser exposure provided with the photosensitive layer containing the copolymer according to the present invention, or the conventional printing plate by UV exposure, both the fingerprint omission phenomenon and scratch resistance In addition, a printing plate excellent in solvent resistance and printing durability could be obtained even when UV ink was used.

Claims (5)

A copolymer having structural units represented by the following formulas (I) and (II), wherein the structural unit represented by the formula (I) is 0.5 to 50% by mass, and the formula (II) An image-forming composition containing a copolymer containing 5 to 60% by mass of the structural unit represented and having a polystyrene calculated weight average molecular weight of 1000 to 200,000 as measured by GPC .

The image-forming composition according to claim 1 , further comprising a photothermal conversion substance that absorbs light and converts it into heat and an alkali-soluble resin. The image forming composition according to claim 2 , wherein the photothermal conversion substance is an infrared absorbent represented by the following formula (III).

(In the formula, each R ₂ independently represents a hydrogen atom or an optionally substituted alkyl group or an alkoxy group, and each R ₃ independently represents an optionally substituted alkyl. A group or an alkoxy group, X represents a charge neutralizing ion, and n represents 5 to 7.) The image forming composition according to claim 1 , further comprising a quinonediazide compound and an alkali-soluble resin. A lithographic printing plate precursor having a photosensitive layer comprising the image forming composition according to any one of claims 1 to 4 on a support.